The Foreign Secretary caused outrage in Moscow when he told the House of Commons that he “would certainly like to see demonstrations outside the Russian embassy” over Moscow’s involvement in the Syrian conflict.

Sir Tony Brenton, who suffered systematic harassment by pro-Kremlin activists when he was ambassador to Moscow between 2004 and 2008, told the Telegraph that the suggestion could provoke “pretty unpleasant” retaliatory measures.

“If we did call for demos in London their instinctive reaction would be similar demonstrations outside our embassy in Moscow,” he said.

“He is a very new foreign secretary and I suspect he never really thought this through. I would hope on reflection he would abandon that line,” he said.

Earlier John Sawers, a former head of MI6, said we should be “mindful of the security of our embassy in Moscow” before calling for demonstrations.

Former head of MI6 John Sawers cautioned against the government calling for demonstrations at the Russian embassy. Credit:
Alastair Grant/AP

Mr Johnson said during an emergency debate on Syria that Russia has committed war crimes by bombing a UN aid convoy and civilian areas of opposition-held eastern Aleppo.

The Russian ministry of defence dismissed Mr Johnson’s comments as "a storm in a glass of muddy London water," and said British "Russophobic hysteria" that should not be dignified with a serious response.

Maj Gen Igor Konashenkov also said there was no evidence to back the claim that Russia was behind the September 20 aid convoy bombing.

In a separate statement, the Kremlin called on Mr Johnson to guarantee the safety of its diplomats under the Vienna convention.

“Great Britain is duty-bound to take responsibility for the safety of Russian diplomatic missions on its territory," Dmitry Peskov, Vladimir Putin’s spokesman, told reporters

The exchange came amid a standoff over Syria that has plunged relations into what some experts have called the most dangerous crisis since the Cold War.

Vladimir Putin on Wednesday accused the West of trying to push a UN resolution on Syria in order to “whip up anti-Russian hysteria.”

Russia vetoed the French draft resolution, which called for an immediate ceasefire, on the weekend. Russia said that Sergey Lavrov, its foreign minister, would meet John Kerry, the US Secretary of State, in Switzerland on Saturday.

It would be the first face to face meeting between the two since the United States suspended diplomatic contact with Russia over the Syrian war on October 3. Russia resumed bombing raids on eastern Aleppo after a pause of several days on Tuesday.

An airstrike on the biggest market there on Wednesday left at least 15 people dead, activists said.

Mr Brenton became the target of a systematic campaign by Nashi, a pro-Kremlin organization, following a series of disagreements between Moscow and London in 2006.

Tactics used by the protesters included following him with banners at weekends, heckling him in meetings, and even advertising his movements on the Internet in a campaign that Mr Brenton said was clearly ordered by the government.

“It was pretty unpleasant,” he said. “When the police tried to intervene, the protestors would show them a bit of paper and the police would back off.”

While a repetition of the 2011 storming of the British embassy in Tehran is unlikely to be repeated in Moscow, embassies there have come under pressure in the past.

In November 2015 a crowd hurled eggs and broke windows at the Turkish embassy in Moscow during a protesting against the shoot down of a Russian jet over Syria by the Turkish air force.